1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or printer and to a toner cartridge for supplying a developer, used in the same.
2. Prior Art
In a conventional image forming apparatus such as an electrophotographic copying machine or printer, a photosensitive body is uniformly charged, and an image is formed on the photosensitive body to form a latent image. The formed latent image is developed with toner to form a toner image which is then transferred to a recording medium or an intermediate transfer material to be further transferred to a recording medium and fixed on the recording medium to form an image.
The developing unit of the image forming apparatus comprises a developing roller and a developer storage chamber having a stirring and mixing unit. When a two-component developer is used, the developer which is prepared by mixing toner with a carrier (magnetic powder) under agitation in the developer storage chamber and is charged is contacted to the developing roller to form a developing brush. The above developing brush is contacted to a latent image formed on the photosensitive body to develop the latent image in order to form a toner image.
Since the toner which is reduced by carrying out development is supplied in this developing unit, the developer storage chamber is loaded with a toner cartridge. To supply the toner, the amount of the remaining toner must be detected. It is possible to know the time of supplying toner by detecting the amount of the remaining developer which is a mixture of toner and a carrier.
In an image forming apparatus which uses a one-component developer, as the amount of the developer is gradually reduced by carrying out development, the developer must be supplied as well.
To cope with this, a developer detector for detecting the amount of the remaining developer is installed in the developer storage chamber. There is suggested a developer detector which displays a warning to urge the supply of toner (developer in the case of a one-component system) or automatically supply toner when the amount of the remaining developer becomes a predetermined amount or less.
There is known a developer detector which comprises a light projecting unit and a light receiving unit in a developer storage chamber and detects the existence of a developer, making use of the fact that a light beam projected from the light projecting unit is cut off by the developer and not input into the light receiving unit when the developer is existent in an optical path from the light projecting unit to the light receiving unit (for example, Official Gazette of Japanese Patent Nos. 3143541 and 2820695).
There is also a developer detector in which a density sensor is installed in a developer storage chamber to automatically supply a developer based on the output signal of the density sensor (for example, Examined Utility Patent Publication No. Hei6-22853).
When the developer storage chamber is loaded with a toner cartridge, the developer is discharged toward the developer storage chamber while it is stirred by a conveyance unit placed in the toner cartridge. As the developer is discharged toward the developer storage chamber, the developer in the toner cartridge is biased. Therefore, the amount of the remaining developer cannot be detected accurately according to the position of the developer detector, thereby causing variations in detection result. The present invention is aimed to solve this problem.
Since the above-described developer storage chamber is part of the developing unit, the developer storage chamber will be referred to “developing unit” including the developer storage chamber in the following description.